How to get to material nodes 2.8
In Blender 2.8x you have the option to switch between workspaces for particular tasks. Blender already includes one for creating materials and it is called Shading. The workspaces are listed as tabs in the top bar.


The benefit of using/creating workspaces is that you don't have to change the layout, create areas or switch editor types for a particular step of your workflow. Instead you can simply switch to a different workspace that is already prepared for the task.
You can of course still change the editor type like in Blender 2.79 and earlier. The editor for materials is the Shader Editor.